A zero-field Cu-NMR study on antiferromagnetic ordered state in four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2

Abstract We report on superconducting and magnetic characteristics in four-layered high- T c superconductors Ba 2 Ca 3 Cu 4 O 8 ( F y O 1 - y ) 2 with apical fluorine through zero-field Cu-NMR measurements. The zero-field NMR spectra shows that the internal magnetic field, induced by antiferromagnetic (AFM) ordered moments, decreases with increasing the local carrier density ( N h ) . The AFM phase expands up to N h ∼ 0.15 , which is the magnetic critical point where the AFM order collapses. Moreover, for y = 1.0 , the AFM order is observed at all CuO 2 layers, although superconducting transition takes place at T c = 55 K . This result suggests that the AFM order uniformly coexists with superconductivity in a single CuO 2 plane in an underdoped region.